While the existing public-switched telecommunications networks can offer access to a number of customer terminals requiring wideband data service, most digital communication within the switched network is limited to 64 Kilobits per second (Kbps) due to the constraints imposed by existing switching systems and transmission facilities.
In those specific applications requiring greater bandwidth, combining several narrowband channels to form a wideband facility between customer terminals via the network has been suggested in the prior art. One problem with these prior art arrangements is that each narrowband channel between customer terminals is established independently of the others, thereby establishing transmission paths with different transmission equipment, different lengths, and different propagation times.
A second problem occurs when the data from grouped channels are not switched through a switching system in the same order as the data was received. This typically occurs when the timem slot interchanger of the switching system causes some, but not all, of the time slot data of a given time frame to be delayed and combined with the time slot data of another time frame.
This second problem is aggravated when more than one stage of time multiplexed switching is utilized in a switching system. The variations in the length of the physical paths between two switching stages associated with the combined channels causes propagation time variations and time slot data misalignment. One prior art arrangement corrected these problems by sending a test signal at the beginning of a call to compute any delay of data from one time frame to another and by introducing delay in selected ones of the narrowband channels to correlate the ddata into its original patterns. In addition to introducing costly equipment to the network, this prior art arrangement does not address the problem of how to correct for any time slot data delay variations that may occur after an initial correction is made.